Multifocal ophthalmic lens

ABSTRACT

A method of designing a multifocal ophthalmic lens with one base focus and at least one additional focus, capable of reducing aberrations of the eye for at least one of the foci after its implantation, comprising the steps of: (i) characterizing at least one corneal surface as a mathematical model; (ii) calculating the resulting aberrations of said corneal surface(s) by employing said mathematical model; (iii) modelling the multifocal ophthalmic lens such that a wavefront arriving from an optical system comprising said lens and said at least one corneal surface obtains reduced aberrations for at least one of the foci. There is also disclosed a method of selecting a multifocal intraocular lens, a method of designing a multifocal ophthalmic lens based on corneal data from a group of patients, and a multifocal ophthalmic lens.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a multifocal ophthalmic lens,and more in detail to a multifocal intraocular lens with reducedaberrations.

TECHNICAL BACKGROUND

[0002] Generally, a multifocal lens is required to provide a certainpower for far vision and different, usually greater (more positive),powers for mid and near vision, the additional power for mid and nearvision sometimes being referred to as “mid-add” and “near-add”, which isusually expressed in dioptres. Multifocal lenses with two foci arereferred to as bifocal.

[0003] Compared with monofocal ophthalmic lenses, multifocal ophthalmiclenses offer the advantage of reduced spectacle dependency, whereaspatients with monofocal lenses generally need reading spectacles. In anideal situation, the patient will have good vision in distance and near,while the depth of focus will enable vision in the intermediate. In thissituation, the patient doesn't need spectacles in any situation.However, since a multifocal lens splits the available light into two ormore foci, the visual quality in each focus is somewhat reduced. When adistant object is focused on the retina, a blurred image is superimposeddue to the presence of the additional foci and vice versa, whichobviously reduces the image quality. The reduced visual quality can bedivided in reduced contrast sensitivity and appearance of opticalphenomena, like straylight and halos. Moreover a patient has to undergoa learning period after implantation, as the two (or more) simultaneousimages displayed on the retina can be confusing in the beginning. Inmost cases, the blurred image is discarded by the human visualperception and retinal processing system.

[0004] Usually, multifocal lenses are designed according to one or moreof the following optical principles:

[0005] 1. Diffractive type: conventional refractive lens combined withdiffractive optics that splits light into two or more focal points.

[0006] 2. Refractive optics with annular zones/rings with differentradii of curvatures.

[0007] Examples of bifocal and multifocal intraocular lenses aredisclosed in U.S. Pat. No. 4,642,112 and U.S. Pat. No. 5,089.024.Examples of commercially available multifocal lenses are: model CeeOn®model 811 E, Pharmacia, Kalamazoo, Mich. and SA 40, AMO, Irvine, Calif.The former is based on diffractive optics, whereby light is partitionedinto two focal points, one for distance vision and one for near vision.The latter is a distance-dominant, zonal-progressive, multifocal opticwith a 3.5-diopter near-add.

[0008] After IOL implantation, any remaining defocus (sphere) andastigmatism (cylinder) can be corrected by spectacles or contact lenses.Beside first order defocus and astigmatism of the eye a number of othervision defects could be present. For example aberrations of differentorders occur when a wavefront passes a refracting surface. The wavefrontitself becomes aspheric when it passes an optical surface that hasimperfections, and vision defects occur when an aspheric wavefront fallson the retina. Both the cornea and the lens in the capsular bagcontribute thus to these types of vision defects if they deviate frombeing perfect or perfectly compensating optical elements. The termaspheric will in this text include both asphericity and asymmetry. Anaspheric surface could be either a rotationally symmetric or arotationally asymmetric surface and/or an irregular surface, i.e. allsurfaces not being spherical.

[0009] Recently, in studies on older subjects, it has been discoveredthat the visual quality of eyes having an implanted monofocal IOL,having spherical lens surfaces (hereafter referred to as a conventionalintraocular lens (CIOL)) is comparable with normal eyes in a populationof the same age. Consequently, a 70 year old cataract: patient can onlyexpect to obtain the visual quality of a non-cataracteous person of thesame age after surgical implantation of an intraocular lens, althoughsuch lenses objectively have been regarded as optically superior to thenatural crystalline lens. This result is explained by the fact thatCIOLs are not adapted to, compensate for defects of the optical systemof the human eye, namely optical aberrations.

[0010] In order to improve the performance of implanted intraocularlenses, efforts have been made to provide intraocular lenses forimplantation that at least partly compensates for such aberrations(Reduced Aberration IOL, or RAIOL). The applicant's own application WO01/89424 discloses an ophthalmic lens providing the eye with reducedaberrations, and a method of obtaining such. The method comprises thesteps of characterizing at least one corneal surface as a mathematicalmodel, calculating the resulting aberrations of said corneal surface(s)by employing said mathematical model, selecting the optical power of theintraocular lens. From this information, an ophthalmic lens is modeledso a wavefront arriving from an optical system comprising said lens andcorneal model obtains reduced aberrations in the eye. The ophthalmiclenses as obtained by the methods are thus capable of reducingaberrations of the eye.

[0011] Of current multifocal lenses, the optical quality is lower thanfor current monofocal lenses. This shows in contrast sensitivitymeasurements on pseudophakic patients. As the visual quality ofmultifocal lenses is relatively low, even minor improvements in opticalquality will lead to visible improvements.

[0012] Both WO 00/76426 and U.S. Pat. No. 6,457,826 mentions thepossibility to make an aspheric BIOL. WO 00/76426 does not disclose useof any specific aspheric characteristic in the lens, but just mentionsthe possibility to combine an asphere with a diffractive pattern.However, U.S. Pat. No. 6,457,826 states that optical corrections can bemade by aspherizing an IOL surface, but it is not at all described howthis could be done. In view of the foregoing, it is therefore apparentthat there is a need for multifocal ophthalmic lenses that are betteradapted to compensate the aberrations caused by the individual surfacesof the eye, such as the corneal surfaces, and capable of bettercorrecting aberrations other than defocus and astigmatism, as isprovided with conventional multifocal intraocular lenses.

SUMMARY OF THE INVENTION

[0013] The object of the invention is to provide a multifocalintraocular lens and a method of designing for designing such, whichovercome the drawbacks of the prior art devices and methods. This isachieved by the method as defined in claims 1, 40 and 81, and by themultifocal ophthalmic lens as defined in claims 102, 103 and 146.

[0014] One advantage with the multifocal intraocular lens according tothe present invention is the improved visual quality that can beobtained.

[0015] Embodiments of the invention are defined in the dependent claims.

SHORT DESCRIPTION OF THE FIGURES

[0016]FIG. 1 shows a calculated Modulation Transfer Function for abifocal intraocular lens according to the present invention and aconventional bifocal lens.

[0017]FIG. 2. shows a measured Modulation Transfer Function for abifocal intraocular lens according to the present invention and aconventional bifocal lens.

[0018]FIG. 3. shows the longitudinal chromatic aberration as a functionof wavelength for the near and far focus.

[0019]FIGS. 4A and 4B. show the Modulation Transfer Function for abifocal intraocular lens according to two embodiments of the presentinvention and according to a conventional bifocal lens.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0020] The present invention generally relates to a multifocalophthalmic lens and to methods of obtaining said multifocal intraocularlens that is capable of reducing the aberrations of the eye for at leastone focus. By aberrations in this context is meant wavefrontaberrations. This is based on the understanding that a convergingwavefront must be perfectly spherical to form a point image, i.e. if aperfect image shall be formed on the retina of the eye, the wavefronthaving passed the optical surfaces of the eye, such as the cornea and anatural or artificial lens, must be perfectly spherical. An aberratedimage will be formed if the wavefront deviates from being spherical. Inthis context the term nonspherical surface will refer to rotationallysymmetric, asymmetric and/or irregular surfaces, i.e. all surfacesdiffering from a sphere. The wavefront aberrations can be expressed inmathematical terms in accordance with different approximate models as isexplained in textbook references, such as M. R. Freeman, Optics, TenthEdition, 1990.

[0021] In a first embodiment, the present invention is directed to amethod of designing a multifocal ophthalmic lens with one base focus andat least one additional focus capable of reducing aberrations of the eyefor at least one of the foci after its implantation. The base focus mayalso be referred to as far field focus and the at least one additionalfocus, as near field focus and mid field focus. The method comprises afirst step of characterizing at least one corneal surface as amathematical model, a second step wherein the mathematical model isemployed for calculating the resulting aberrations of the cornealsurface. An expression of the corneal aberrations is thereby obtained,i.e. the wavefront aberrations of a spherical wavefront having passedsuch a corneal surface. Dependent on the selected mathematical modeldifferent routes to calculate the corneal aberrations can be taken. Thecorneal surfaces are preferably characterized as mathematical models andthe resulting aberrations of the corneal surfaces are calculated byemploying the mathematical models and raytracing techniques. Anexpression of the corneal wavefront aberrations is thereby obtained,i.e. the wavefront aberrations of a wavefront having passed such acorneal surface. Dependent on the selected mathematical model differentroutes to calculate the corneal wavefront aberrations can be taken.Preferably, the corneal surfaces are characterized as mathematicalmodels in terms of a conoid of rotation or in terms of polynomials or acombination thereof. More preferably, the corneal surfaces arecharacterized in terms of linear combinations of polynomials.

[0022] From the information of steps above an ophthalmic lens ismodeled, such that a wavefront from an optical system comprising saidlens and corneal model obtains reduced aberrations. The optical systemconsidered when modeling the lens typically includes the cornea and saidlens, but in the specific case it can also include other opticalelements including the lenses of spectacles, or an artificial correctionlens, such as a contact lens, a corneal inlay implant or an implantablecorrection lens depending on the individual situation.

[0023] Furthermore the base power for far vision, the light distributionbetween the at least two foci, and the optical power(s) for theadditional focus/foci, of the ophthalmic lens has to be selected, whichis done according to conventional methods for the specific need ofoptical correction of the eye, for example the method described in U.S.Pat. No. 5,968,095.

[0024] Modeling the multifocal lens involves selection of one or severallens parameters in a system which contributes to determine the lensshape for given, pre-selected refractive powers. This typically involvesthe selection of conventional lens parameters such as the anteriorradius and surface shape, posterior radius and surface shape, the lensthickness and the refractive index of the lens, as well as parametersspecific for multifocal lenses. As mentioned above there are a number ofdifferent ways by which to multifocal lenses may be designed. Hence, themultifocal specific parameters depend on what multifocal design that isused.

[0025] The multifocal ophthalmic lens according to the present inventioncan be realized in the form of a multifocal contact lens, a multifocalcorneal inlay for aphakic patients, or the like, but it will bedescribed in detail in the form of a multifocal intraocular lens.Furthermore the multifocal specific parameters discussed will be limitedto parameters applicable on bifocal lenses of diffractive type, but itshould be understood that the multifocal lens modeled according topresent invention can be of any multifocal type or combinations thereof.A bifocal diffractive lens is a combination of a conventional refractivelens and a diffractive lens, the former focused to infinity and thelatter for near vision. A diffractive lens consists of a series ofradial rings or “zones” of decreasing width. Typically, the lightdistribution of a bifocal diffractive lens is set at around 50:50%, thusboth the near and the far foci are accommodated. The diffractive lensmay be formed on the anterior or posterior surface of the conventionallens, or at an intermediate position. The light distribution of thediffractive bifocal lens is determined by the step height of thediffractive zones. The power add for near field focus is determined bythe diameters of the diffractive zones. Theoretically, this isindependent of the refractive indices of the lens and the surroundingmedium.

[0026] In practical terms, the lens modeling can be performed with databased on a conventional bifocal lens, such as the CeeOn® 811 E lens fromPharmacia Corp. Values of the central radii of the lens, its thicknessand refractive index are maintained, while selecting a different shapeof the anterior and/or posterior surface, thus providing one or both ofthese surfaces to have a nonspherical shape.

[0027] According to one embodiment of the present invention, theanterior and/or posterior surface of the bifocal intraocular lens ismodeled by selecting a suitable aspheric component. Preferably the lenshas at least one surface described as a nonsphere or other conoid ofrotation. Designing nonspherical surfaces of lenses is a well-knowntechnique and can be performed according to different principles and thedescription of such surfaces is explained in more detail in our PCTpatent application WO 01/62188, to which is given reference.

[0028] The inventive method can be further developed by comparingwavefront aberrations of an optical system comprising the lens and themodel of the average cornea with the wavefront aberrations of theaverage cornea and evaluating if a sufficient reduction in wavefrontaberrations is obtained for at least one of the foci. Suitable variableparameters are found among the above-mentioned physical parameters ofthe lens, which can be altered so as to find a lens model, whichdeviates sufficiently from being a spherical lens to compensate for thecorneal aberrations.

[0029] The characterization of at least one corneal surface as amathematical model and thereby establishing a corneal model expressingthe corneal wavefront aberrations is preferably performed by directcorneal surface measurements according to well-known topographicalmeasurement methods which serve to express the surface irregularities ofthe cornea in a quantifiable model that can be used with the inventivemethod. Corneal measurements for this purpose can be performed by theORBSCAN® videokeratograph, as available from Orbtech, or by cornealtopography methods, such as EyeSys® from Premier Laser Systems.Preferably, at least the front corneal surface is measured and morepreferably both front and rear corneal surfaces are measured andcharacterized and expressed together in resulting wavefront aberrationterms, such as a linear combination of polynomials which represent thetotal corneal wavefront aberrations. According to one important aspectof the present invention, characterization of corneas is conducted on aselected population with the purpose of expressing an average of cornealwavefront aberrations and designing a lens from such averagedaberrations. Average corneal wavefront aberration terms of thepopulation can then be calculated, for example as an average linearcombination of polynomials and used in the lens design method. Thisaspect includes selecting different relevant populations, for example inage groups, to generate suitable average corneal surfaces.Advantageously, lenses can thereby be provided which are adapted to anaverage cornea of a population relevant for an individual elected toundergo cataract surgery or refractive correction surgery includingimplantation of an IOL or corneal inlays or phakic IOLs. The patientwill thereby obtain a bifocal lens that gives the eye substantially lessaberrations when compared to a conventional spherical lens.

[0030] Preferably, the mentioned corneal measurements also include themeasurement of the corneal refractive power. The power of the cornea andthe axial eye length are typically considered for the selection of thelens power in the inventive design method.

[0031] Also preferably, the wavefront aberrations herein are expressedas a linear combination of polynomials and the optical system comprisingthe corneal model and modeled intraocular lens provides, for at leastone of the foci and preferably for each foci, a wavefront havingobtained a substantial reduction in aberrations, as expressed by one ormore such polynomial terms. In the art of optics, several types ofpolynomials are available to skilled persons for describing aberrations.Suitably, the polynomials are Seidel or Zernike polynomials. Accordingto the present invention Zernike polynomials preferably are employed.

[0032] The technique of employing Zernike terms to describe wavefrontaberrations originating from optical surfaces deviating from beingperfectly spherical is a state of the art technique and can be employedfor example with a Hartmann-Shack sensor as outlined in J. Opt. Soc.Am., 1994, Vol. 11(7), pp. 1949-57. It is also well established amongoptical practitioners that the different Zernike terms signify differentaberration phenomena including defocus, astigmatism, coma and sphericalaberration up to higher aberrations. In an embodiment of the presentmethod, the corneal surface measurement results in that a cornealsurface is expressed as a linear combination of the first 15 Zernikepolynomials. By means of a raytracing method, the Zernike descriptioncan be transformed to a resulting wavefront (as described in Equation(1)), wherein Z_(i) is the i-th Zernike term and a_(i) is the weightingcoefficient for this term. Zernike polynomials are a set of completeorthogonal polynomials defined on a unit circle. Below, Table 1 showsthe first 15 Zernike terms and the aberrations each term signifies.$\begin{matrix}{{z\left( {\rho,\theta} \right)} = {\sum\limits_{i = 1}^{15}{a_{i}Z_{i}}}} & (1)\end{matrix}$

[0033] In equation (1), ρ and θ represent the normalized radius and theazimuth angle, respectively. TABLE 1 Z_(i)(ρ,θ) i 1 1 Piston 2 2ρcos θTilt x 3 2ρsinθ Tilt y 4 {square root over (3)}(2ρ² − 1) Defocus 5{square root over (6)}(ρ² sin 2θ) Astigmatism 1^(st) order (45°) 6{square root over (6)}(ρ² cos 2θ) Astigmatism 1^(st) order (0°) 7{square root over (8)}(3ρ³ − 2ρ)sin θ Coma y 8 {square root over(8)}(3ρ³ − 2ρ)cos θ Coma x 9 {square root over (8)}(ρ³ sin 3θ) Trifoil30° 10 {square root over (8)}(ρ³ cos 3θ) Trifoil 0° 11 {square root over(5)}(6ρ⁴ − 6ρ² + 1) Spherical aberration 12 {square root over (10)}(4ρ⁴− 3ρ²)cos 2θ Astigmatism 2^(nd) order (0°) 13 {square root over(10)}(4ρ⁴ − 3ρ²)sin 2θ Astigmatism 2^(nd) order (45°) 14 {square rootover (10)}(ρ⁴ cos 4θ) Tetrafoil 0° 15 {square root over (10)}(ρ⁴ sin 4θ)Tetrafoil 22.5°

[0034] Conventional optical correction with intraocular lenses will onlycomply with the fourth term of an optical system comprising the eye withan implanted lens. Glasses, contact lenses and some special intra ocularlenses provided with correction for astigmatism can further comply withterms five and six and substantially reducing Zernike polynomialsreferring to astigmatism.

[0035] The inventive method further includes to calculate the wavefrontaberrations resulting from an optical system comprising said modeledbifocal intraocular lens and cornea and expressing it in a linearcombination of polynomials and to determine if the bifocal intraocularlens has provided sufficient reduction in wavefront aberrations for oneor more of the foci. If the reduction in wavefront aberrations is foundto be insufficient, the lens will be re-modeled until one or several ofthe polynomial terms are sufficiently reduced. Remodeling the lens meansthat at least one lens design parameter affecting one or more of thefoci is changed. These include the anterior surface shape and centralradius, the posterior surface shape and central radius, the thickness ofthe lens, its refractive index, and the diameters and the step height ofthe diffractive zones. Typically, such remodeling includes changing theshape of a lens surface so it deviates from being spherical. There areseveral tools available in lens design that are useful to employ withthe design method, such as the optical design software packages OSLO andCode-V. The formats of the Zernike polynomials associated with thisapplication are listed in Table 1.

[0036] According to one embodiment, the inventive method comprisesexpressing at least one corneal surface as a linear combination ofZernike polynomials and thereby determining the resulting cornealwavefront Zernike coefficients, i.e. the coefficient of each of theindividual Zernike polynomials that is selected for consideration. Thebifocal lens is then modeled so that an optical system comprising ofsaid model bifocal lens and cornea provides a wavefront having asufficient reduction of selected Zernike coefficients for at least oneof the foci. The method can optionally be refined with the further stepsof calculating the Zernike coefficients of the Zernike polynomialsrepresenting a wavefront resulting from an optical system comprising themodeled intraocular bifocal lens and cornea and determining if the lenshas provided a sufficient reduction of the wavefront Zernikecoefficients for at least one foci of the optical system of cornea andlens; and optionally re-modeling said bifocal lens until a sufficientreduction in said coefficients is obtained for the at least one foci.Preferably, in this aspect the method considers Zernike polynomials upto the 4^(th) order and aims to sufficiently reduce Zernike coefficientsreferring to spherical aberration and/or astigmatism terms. It isparticularly preferable to sufficiently reduce the 11^(th) Zernikecoefficient of a wavefront from an optical system comprising cornea andsaid modeled multifocal intraocular lens, so as to obtain an eyesufficiently free from spherical aberration for at least one of thefoci. Alternatively, the design method can also include reducing higherorder aberrations and thereby aiming to reduce Zernike coefficients ofhigher order aberration terms than the 4^(th) order.

[0037] To achieve the desired reduction of aberrations, the bifocalintraocular lens is optimized with respect to unabberrated opticalbehavior of the optical system of the eye. In this respect, the opticalbehavior may be optimized for either one of the foci or bothsimultaneously. If the lens is optimized for the base focus, then thelens will give best optical result for far vision. Consequently when thelens is optimized for the near focus, the best performance is achievedin the near vision. Best over all performance is achieved when the lensis simultaneously optimized for both foci. The diffractive pattern ofthe bifocal lens may be formed independently of the lens surface that ismodeled to reduce aberrations of the optical system, but it could alsobe formed on the same lens surface.

[0038] When designing lenses based on corneal characterizations from aselected population, preferably the corneal surfaces of each individualare expressed in Zernike polynomials describing the surface topographyand there from the Zernike coefficients of the wavefront aberration aredetermined. From these results average Zernike wavefront aberrationcoefficients are calculated and employed in the design method, aiming ata sufficient reduction of selected such coefficients. In an alternativemethod according to the invention, average values of the Zernikepolynomials describing the surface topography are instead calculated andemployed in the design method. It is to be understood that the resultinglenses arriving from a design method based on average values from alarge population have the purpose of substantially improving visualquality for all users. A lens having a total elimination of a wavefrontaberration term based on an average value may consequently be lessdesirable and leave certain individuals with an inferior vision thanwith a conventional lens. For this reason, it can be suitable to reducethe selected Zernike coefficients only to certain degree or to apredetermined fraction of the average value.

[0039] According to another approach of the inventive design method,corneal characteristics of a selected population and the resultinglinear combination of polynomials, e.g. Zernike polynomials, expressingeach individual corneal aberrations can be compared in terms ofcoefficient values. From this result, a suitable value of thecoefficients is selected and employed in the inventive design method fora suitable lens. In a selected population having aberrations of the samesign such a coefficient value can typically be the lowest value withinthe selected population and the lens designed from this value wouldthereby provide improved visual quality for all individuals in the groupcompared to a conventional lens.

[0040] One embodiment of the method comprises selecting a representativegroup of patients and collecting corneal topographic data for eachsubject in the group. The method comprises further transferring saiddata to terms representing the corneal surface shape of each subject fora preset aperture size representing the pupil diameter. Thereafter amean value of at least one corneal surface shape term of said group iscalculated, so as to obtain at least one mean corneal surface shapeterm. Alternatively or complementary a mean value of at least one to thecornea corresponding corneal wavefront aberration term can becalculated. The corneal wavefront aberration terms are obtained bytransforming corresponding corneal surface shape terms using a raytraceprocedure. From said at least one mean corneal surface shape term orfrom said at least one mean corneal wavefront aberration term an bifocalintraocular lens capable of reducing, for at least one of its foci, saidat least one mean wavefront aberration term of the optical systemcomprising cornea and lens is designed.

[0041] In one preferred embodiment of the present invention the methodfurther comprises designing an average corneal model for the group ofpeople from the calculated at least one mean corneal surface shape termor from the at least one mean corneal wavefront aberration term. It alsocomprises checking that the designed ophthalmic lens compensatescorrectly for the at least one mean aberration term. This is done bymeasuring these specific aberration terms of a wavefront having traveledthrough the model average cornea and the lens. The lens is redesigned ifsaid at least one aberration term has not been sufficiently reduced inthe measured wavefront for at least one of the foci.

[0042] Preferably one or more surface descriptive (asphericitydescribing) constants are calculated for the bifocal lens to be designedfrom the mean corneal surface shape term or from the mean cornealwavefront aberration terms for a predetermined radius. The sphericalradius is determined by the refractive power of the lens.

[0043] The corneal surfaces are preferably characterized as mathematicalmodels and the resulting aberrations of the corneal surfaces arecalculated by employing the mathematical models and raytracingtechniques. An expression of the corneal wavefront aberrations isthereby obtained, i.e. the wavefront aberrations of a wavefront havingpassed such a corneal surface. Dependent on the selected mathematicalmodel different routes to calculate the corneal wavefront aberrationscan be taken. Preferably, the corneal surfaces are characterized asmathematical models in terms of a conoid of rotation or in terms ofpolynomials or a combination thereof. More preferably, the cornealsurfaces are characterized in terms of linear combinations ofpolynomials.

[0044] In one embodiment of the invention, the at least one nonsphericalsurface of the bifocal lens is designed such that the lens for at leastone focus, in the context of the eye, provides to a passing wavefront atleast one wavefront aberration term having substantially the same valuebut with opposite sign to a mean value of the same aberration termobtained from corneal measurements of a selected group of people, towhich said patient is categorized. Hereby a wavefront arriving from thecornea of the patient's eye obtains a reduction in said at least oneaberration term provided by the cornea after passing said bifocal lens.The used expression ‘in the context of the eye’ can mean both in thereal eye and in a model of an eye.

[0045] In a specific embodiment of the invention, the wavefront obtainsreduced aberration terms expressed in rotationally symmetric Zerniketerms up to the fourth order. For this purpose, the surface of thebifocal intraocular lens is designed to reduce a positive sphericalaberration term of a passing wavefront for at least one of the foci. Inthis text positive spherical aberration is defined such that a sphericalsurface with positive power produces positive spherical aberration.Preferably the bifocal lens is adapted to compensate for sphericalaberration for at least one of the foci, and more preferably it isadapted to compensate for at least one term of a Zernike polynomialrepresenting the aberration of a wavefront, preferably at least the11^(th) Zernike term, see Table 1.

[0046] The selected groups of people could for example be a group ofpeople belonging to a specific age interval, a group of people who willundergo a cataract surgical operation or a group of people who haveundergone corneal surgery including but not limited to LASIK (laser insitu keratomileunsis), RK (radialo keratoectomy) or PRK (photorefractivekeratoectomy). The group could also be a group of people who have aspecific ocular disease or people who have a specific ocular opticaldefect.

[0047] The lens is also suitably provided with optical powers. This isdone according to conventional methods for the specific need of opticalcorrection of the eye. Preferably the refractive power for the basefocus of the lens is less than or equal to 34 diopters and theadditional focus between 2 and 6 diopters. An optical system consideredwhen modeling the lens to compensate for aberrations typically includesthe average cornea and said lens, but in the specific case it can alsoinclude other optical elements including the lenses of spectacles, or anartificial correction lens, such as a contact lens, a corneal inlay oran implantable correction lens depending on the individual situation.

[0048] In an especially preferred embodiment the bifocal intraocularlens is designed for people who will undergo a cataract surgery. In thiscase it is has been shown that the average cornea from such a populationis represented by a prolate surface following the formula:$z = {\frac{\left( \frac{1}{R} \right)r^{2}}{1 + \sqrt{1 - {\left( \frac{1}{R} \right)^{2}\left( {{cc} + 1} \right)r^{2}}}} + {{ad}\quad r^{4}} + {{ae}\quad r^{6}}}$

[0049] wherein,

[0050] the conical constant cc has a value ranging between −1 and 0

[0051] R is the central lens radius and

[0052] ad and ae are polynomial coefficients additional to the conicalconstant.

[0053] In these studies the conic constant of the prolate surface rangesbetween about −0.05 for an aperture size (pupillary diameter) of 4 mm toabout −0.18 for an aperture size of 7 mm. According to these results thebifocal intraocular lens to be designed should have a prolate surfacefollowing the same formula. Accordingly a bifocal intraocular lenssuitable to improve visual quality by reducing at least sphericalaberration for at least one focus for a cataract patient based on anaverage corneal value will have a prolate surface following the formulaabove. Since the cornea generally produces a positive sphericalaberration to a wavefront in the eye, a bifocal intraocular lens forimplantation into the eye will have negative spherical aberration termswhile following the mentioned prolate curve. As will be discussed inmore detail in the exemplifying part of the specification, it has beenfound that an intraocular lens that can correct for 100% of a meanspherical aberration has a conical constant (cc) with a value of lessthan 0 (representing a modified conoid surface). For example, a 6 mmdiameter aperture will provide a 20 diopter lens with conical constantvalue of about −1.02.

[0054] In this embodiment, the bifocal intraocular lens is designed tobalance the spherical aberration of a cornea that has a Zernikepolynomial coefficient representing spherical aberration of thewavefront aberration with a value in the interval from 0.0000698 mm to0.000871 mm for a 3 mm aperture radius, 0.0000161 mm to 0.00020 mm for a2 mm aperture radius, 0.0000465 mm to 0.000419 mm for a 2,5 mm apertureradius and 0.0000868 mm to 0.00163 mm for a 3.5 mm aperture radius usingpolynomials expressed in table 1. These values were calculated for amodel cornea having two surfaces with a refractive index of the corneaof 1.3375. It is possible to use optically equivalent model formats ofthe cornea without departing from the scope of the invention. Forexample one or more multiple surface corneas or corneas with differentrefractive indices could be used. The lower values in the intervals arehere equal to the measured average value for that specific apertureradius minus one standard deviation. The higher values are equal to themeasured average value for each specific aperture radius plus threestandard deviations. The reason for selecting only minus one SD(=Standard Deviation) while selecting plus three SD is that in thisembodiment it is convenient to only compensate for positive cornealspherical aberration and more than minus one SD added to the averagevalue would give a negative corneal spherical aberration.

[0055] According to one embodiment of the invention the method furthercomprises the steps of measuring the at least one wavefront aberrationterm of one specific patient's cornea and determining if the selectedgroup corresponding to this patient is representative for this specificpatient. If this is the case the selected lens is implanted and if thisis not the case a lens from another group is implanted or an individuallens for this patient is designed using this patient's cornealdescription as a design cornea. These method steps are preferred sincethen patients with extreme aberration values of their cornea can begiven special treatments.

[0056] According to another embodiment, the present invention isdirected to the selection of a bifocal intraocular lens of refractivepowers, suitable for the desired optical correction that the patientneeds, from a plurality of lenses having the same powers but differentaberrations. The selection method is similarly conducted to what hasbeen described with the design method and involves the characterizing ofat least one corneal surface with a mathematical model by means of whichthe aberrations of the corneal surface is calculated. The optical systemof the selected lens and the corneal model is then evaluated so as toconsider if sufficient a reduction in aberrations is accomplished for atleast one foci by calculating the aberrations of a wavefront arrivingfrom such a system. If an insufficient correction is found a new lens isselected, having the same powers, but different aberrations. Themathematical models employed herein are similar to those described aboveand the same characterization methods of the corneal surfaces can beemployed.

[0057] Preferably, the aberrations determined in the selection areexpressed as linear combinations of Zernike polynomials and the Zernikecoefficients of the resulting optical system comprising the model corneaand the selected lens are calculated. From the coefficient values of thesystem, it can be determined if the bifocal intraocular lens hassufficiently balanced the corneal aberration terms for at least onefoci, as described by the Zernike coefficients of the optical system. Ifno sufficient reduction of the desired individual coefficients is found,these steps can be iteratively repeated by selecting a new lens of thesame powers but with different aberrations, until a lens capable ofsufficiently reducing the aberrations of the optical system for at leastone foci is found. Preferably at least 15 Zernike polynomials up to the4^(th) order are determined. If it is regarded as sufficient to correctfor spherical aberration, only the spherical aberration terms of theZernike polynomials for the optical system of cornea and bifocalintraocular lens are corrected. It is to be understood that the bifocalintraocular lens shall be selected so a selection of these terms becomesufficiently small for the optical system comprising lens and cornea forat least one of the foci. In accordance with the present invention, the11^(th)

[0058] Zernike coefficient, a₁₁, can be substantially eliminated orbrought sufficiently close to zero for at least one of the foci. This isa prerequisite to obtain a bifocal intraocular lens that sufficientlyreduces the spherical aberration of the eye for at least one of thefoci. The inventive method can be employed to correct for other types ofaberrations than spherical aberration by considering other Zernikecoefficients in an identical manner, for example those signifyingastigmatism, coma and higher order aberrations. Also higher orderaberrations can be corrected dependent on the number of Zernikepolynomials elected to be a part of the modeling, in which case a lenscan be selected capable of correcting for higher order aberrations thanthe 4^(th) order.

[0059] According to one important aspect, the selection method involvesselecting lenses from a kit of lenses having lenses with a range ofpowers and a plurality of lenses within each power combinations for farand near foci having different aberrations. In one example the lenseswithin each power combination have anterior surfaces with differentaspherical components. If a first lens does not exhibit sufficientreduction in aberration for at least one of the foci, as expressed insuitable Zernike coefficients, then a new lens of the same powercombination, but with a different surface (aspheric component) isselected. The selection method can if necessary be iteratively repeateduntil the best lens is found or the studied aberration terms are reducedbelow a significant borderline value for at least one of the foci. Inpractice, the Zernike terms obtained from the corneal examination willbe directly obtained by the ophthalmic surgeon and by means of analgorithm they will be compared to known Zernike terms of the lenses inthe kit. From this comparison the most suitable lens in the kit can befound and implanted. Alternatively, the method can be conducted beforecataract surgery and data from the corneal estimation is sent to a lensmanufacturer for production of an individually tailored lens.

[0060] The present invention further pertains to a bifocal intraocularlens having at least one nonspherical surface capable of transferring,for at least one foci, a wavefront having passed through the cornea ofthe eye into a substantially spherical wavefront with its center at theretina of the eye. Preferably, the wavefront is substantially sphericalwith respect to aberration terms expressed in rotationally symmetricZernike terms up to the fourth order.

[0061] In accordance with an especially preferred embodiment, theinvention relates to a bifocal intraocular lens, which has at least onesurface, when expressed as a linear combination of Zernike polynomialterms using the normalized format, that has a negative 11th term of thefourth order with a Zernike coefficient a₁₁ that that can balance apositive corresponding term of the cornea, to obtain sufficientreduction of the spherical aberration for at least one foci of the eyeafter implantation. In one aspect of this embodiment, the Zernikecoefficient a₁₁ of the bifocal lens is determined so as to compensatefor an average value resulting from a sufficient number of estimationsof the Zernike coefficient a₁₁ in several corneas. In another aspect,the Zernike coefficient a,, is determined to compensate for theindividual corneal coefficient of one patient. The bifocal lens canaccordingly be tailored for an individual with high precision.

[0062] The invention further relates to another method of providing apatient with a bifocal intraocular lens, which at least partlycompensates for the aberrations of the eye for at least one of the foci.This method comprises removing the natural lens from the eye. Surgicallyremoving of the impaired lens can be performed by using a conventionalphacoemulsification method. The method further comprises measuring theaberrations of the aphakic eye, not comprising the a lens, by using awavefront sensor. Suitable methods for wavefront measurements are foundin J.Opt.Soc.Am., 1994, Vol. 11(7), pp. 1949-57 by Liang et. al.Furthermore, the method comprises selecting from a kit of lenses a lensthat at least partly compensates for the measured aberrations for atleast one of the foci and implanting said lens into the eye. The kit oflenses comprises lenses of different powers and different aberrationsand finding the most suitable lens can be performed in a manner asearlier discussed. Alternatively, an individually designed lens for thepatient can be designed based on the wavefront analysis of the aphakiceye for subsequent implantation. This method is advantageous, since notopographical measurements of the cornea are need to be done and thewhole cornea, including the front and back surfaces, is automaticallyconsidered.

[0063] According to a special embodiment of the present invention theaspheric multifocal lenses designed to reduce aberrations of wavefrontsin the foci arriving from a system of the lens and cornea, as describedin the foregoing parts, can provided with means to distribute lightamong the foci with purpose of providing the wearer of the lens with abetter functional vision. For example, it is desirable to provide thefar focus of an aspheric bifocal aberration reducing IOL with more lightintensity when the pupil is its maximum diameter. In practical termsthis will provide an individual with better visual quality of distantobjects in darkness, so driving during night is simplified. There areseveral known techniques to modify the light distribution of multifocallenses by reducing the step height of the diffractive pattern in thedirection towards the periphery of lens. U.S. Pat. No. 4,881,805suggests different routes to use different echelette depth to vary thelight intensity among the different foci of a multifocal lens. U.S. Pat.No. 5,699,142 discloses a multifocal intraocular lens with a diffractivepattern having an apodization zone that gradually shifts the energybalance from the near focus to the distant focus. The apodization zoneis construed so that the echelettes of the diffractive pattern graduallyhas a reduced depth towards the lens periphery. By making an appropriateadjustment of the step height (echelette depth), a desired deviationfrom 50-50% distribution between the two foci of a bifocal lens can beobtained.

[0064] According to another special embodiment, the aspheric multifocallenses of the present invention as outlined in the previous parts of thespecification can be provided with means to reduce chromatic aberrationin at least one of its foci. Aspheric monofocal lenses with a capacityto correct both chromatic aberration and other aberrations as induced bythe optical parts of the eye and distort vision has been described inthe International patent application published as WO 02/084281 whichhereby is incorporated as a reference. In this context “chromaticaberration” signifies both monochromatic and chromatic aberrationintroduced by the optical surfaces of eye and eventually also the lensitself.

[0065] The multifocal intraocular lenses can generally be of arefractive or a diffractive type of the diffractive type has beendescribed elsewhere in greater detail. For both alternatives ofmultifocal IOLs, the chromatic aberration preferably is provided by asurface configured as a diffractive part with a diffractive surfacepattern and has a refractive power to be added to the total lens power.In both alternatives, chromatic aberration reducing surface is designedto compensate for any chromatic aberration introduced by the refractivepart of lens and for monochromatic aberrations introduced by saiddiffractive surface pattern. As is discussed in WO 02/084281, it ispossible to design the lens to reduce chromatic aberration determinedfrom individual eye surface (i.e. corneas), or to reduce an averagedchromatic aberration value collected from relevant group of individuals(e.g. a mean value from corneas of patients elected to undergo cataractsurgery).

[0066] In the design process of an aspheric multifocal IOL that iscapable of correcting both for chromatic aberrations and otheraberrations, such as spherical aberrations, it may also be needed tocompensate for other aberrations, such as spherical aberrationsintroduced by the diffractive pattern, while performing optionaladjustments of the power contribution of the diffractive pattern.

[0067] For the example where the asphericity compensate for aberrationterms, such as spherical aberration the features providing the lens withmultiple foci already are set, the design process preferably wouldinclude the steps of:

[0068] (i) selecting an eye model, suitably the eye model of Navarro(1985), with an aspheric multifocal ophthalmic lens of a predeterminedrefractive power and a predetermined amount of at least onemonochromatic aberration;

[0069] (ii) estimating the power of said eye model at differentwavelengths, so as to determine the chromatic aberration of the eyemodel;

[0070]1(iii) estimating a correction function of how the power varieswith the wavelength to be an ideal compensation for said chromaticaberration of the eye model;

[0071] (iv) finding a linear function of how power varies with thewavelength, which suitably approximates said correction function;

[0072] (v) calculating a provisional zone width of a diffractive profilecorresponding to this linear function and also calculating thediffractive power of this diffractive profile;

[0073] (vi) reducing the refractive power of the lens by the amount ofpower calculated for the diffractive profile;

[0074] (vii) estimating a new correction function of step iii), findinga new linear function of step iv) and calculating a new provisional zonewidth and a new diffractive power for a new diffractive profilecorresponding to this new linear function;

[0075] (viii) adjusting the refractive power of the lens such that thetotal power equals the predetermined power;

[0076] (ix) repeating steps vii) to viii) until a suitable combinationof a refractive and a diffractive part of the hybrid ophthalmic lens isfound that both provide the eye model with a predetermined power andwith a suitable reduction in chromatic aberration.

[0077] In the design process it is preferable for a diffractive bifocallens to balance the chromatic aberration between the near and thedistant foci in a manner that resulting lens in a Navarro eye modelobtains polychromatic modulation transfer functions at 50 cycles/mm froma set eye model which approaches the same value (see also Example 4,below) For the embodiment with a diffractive aspheric multifocal IOL,the diffractive surface pattern correcting for chromatic aberration willbe a second diffractive pattern that consists of a number of rings. Forthe example, a lens having a total 20 D power with a 2 D power comingfrom the second diffractive pattern, the first zone has a radial widthof 1.5 mm. In this case, the second diffractive surface pattern islocated on the anterior side of the lens superimposed on the sphericalsurface. Preferably, the first diffractive pattern then is located onthe posterior side of the lens. Also, for a refractive bifocal lens, thechromatic aberration is (slightly) different for the near and far focus,which means that the performance of the near and far focus can bebalanced, using a merit function, of which the modulation transferfunctions at 50 c/mm is an example.

[0078] In another special embodiment, the multifocal lens modelled toreduce aberrations of at least of the foci in a optical systemcomprising the lens and a model cornea without taking considerations toaberrations that the cornea will provide a wavefront with when passingthe system. This type of lenses will be suitable for individuals withcorneas that generate few aberrations or when there is not access to anycorneal aberration data. These lenses will be designed with anonspherical surface with a surface design construed to reduceaberrations in a wavefront passing said lens that are generated from thelens itself. Typically, such aberrations involve spherical aberration. Asuitable example of this type of multifocal lens is of the diffractivetype having a diffractive pattern on the lens surface that is capable ofgenerating multiple foci, and more preferably it is a bifocal lens thatdistributes more light to its distant focus than to its near focus.Optionally, it can be provided with the mentioned means to generate adesired light distribution and with a second diffractive pattern tocompensate for chromatic aberrations of the eye

[0079] The lenses according to the present invention can be manufacturedwith conventional methods. In one embodiment they are made from soft,resilient material, such as silicones or hydrogels. Examples of suchmaterials suitable for foldable intraocular lenses are found in U.S.Pat. No. 5,444,106 or in U.S. Pat. No. 5,236,970. Manufacturing ofnonspherical silicone lenses or other foldable lenses can be performedaccording to U.S. Pat. No. 6,007,747. Alternatively, the lensesaccording to the present invention can be made of a more rigid material,such as poly(methyl)methacrylate. The skilled person can readilyidentify alternative materials and manufacturing methods, which will besuitable to employ to produce the inventive aberration reducing lenses.

[0080] As is shown in the following examples, the bifocal intraocularlens according to the present invention (BRAIOL) outperformsconventional BIOLs with respect to Modulation Transfer Functioncharacteristics. More specifically it has been found that the BRAIOL hasa modulation of at least 0.2 for both foci at a spatial frequency of 50cycles per millimetre, when designed such that the light distributionbetween the two foci is 50:50%. The measurements are performed in anaverage eyemodel using a 5mm aperture. Surprisingly it has further beenfound that the sum of the modulation at 50 c/mm for the two or more fociis more than 0.40, and in some cases even above 0.50, independent of thelight distribution, when measured in the model specified above. The factthat the sum of the modulation at 50 c/mm is independent of lightdistribution is illustrated for the case where the light distributionhas a limiting value of 100:0%, which is equivalent to a monofocal lens.Conventional lenses and lenses correcting spherical aberration weredesigned, manufactured and measured. In this situation, the conventionallens has a modulation at 50 c/mm of 0.21, while the design optimized forspherical aberration shows a modulation of 0.6, equivalent to the sum ofthe designed bifocal lens.

[0081] Furthermore, the evaluation experiments have revealed that thewavefronts of the 2 foci of a bifocal lens are independent with respectto some of the Zernike terms, but that some of the Zernike terms arecoupled or equal for both. The far majority of this difference is in the‘defocus’ term, which represents the 4 diopters difference between thefocal points. In the design process it has been found that the sphericalaberration part of the wavefront is not very different for the 2wavefronts. This is also true for all other aberrations, apart fromdefocus, tilt and the piston term. Consequently the present inventionmakes it possible to provide a lens with reduced aberrations inessentially the same scale for all foci.

EXAMPLES

[0082] General

[0083] A bifocal intraocular lens which corrects the corneal sphericalaberration (BRAIOL) can be modeled based on a conventional bifocal lens(BIOL), in this case the bifocal model 811E, Pharmacia Corp., which is adiffractive lens design made of Poly(MethylMethAcrylate) material. Thepower add of this lens is +4 diopter for reading, which corresponds toreading spectacles of 3 diopters. In this example, the design is adaptedto be used for a silicone material. As a consequence, the step heightsof the diffractive surface profile are increased with the ratio of thereduced refractive indices of the 2 materials.

[0084] The lens optic is a combination of a biconvex lens and adiffractive lens. The diffractive surface profile is superimposed ontothe spherical posterior surface of the optic. The diffractive surfaceprofile can be described using conventional sag equations. Examples ofequations for the surface profile are described in the literature. Forinstance, Cohen (1993, ‘Diffractive bifocal lens design’, Optom Vis Sci70(6): 461:8) describes the diffractive profile with the equation:

S _(d)(r)=h*{N−r ² /w ²}

[0085] wherein

[0086] r is the distance from the optical axis

[0087] h is the maximum profile height (stepheight)

[0088] N is the zone number

[0089] w is the width of the first zone

[0090] Other equations are also possible. The type of diffractiveprofile is not relevant for the working principles. The diffractiveprofile is superimposed onto a normal spherical surface, so that thetotal sag equation becomes

S(r)=S _(s)(r)+S _(d)(r),

[0091] where S_(s)(r) is the sag equation of a spherical biconvex lens:${S_{s}(r)} = \frac{{cv}*r^{2}}{1 + \sqrt{1 - {{cv}^{2}*r^{2}}}}$

[0092] cv=1/R is the curvature of the lens optic

[0093] R is the radius of curvature of the lens optic

[0094] The radius of curvature of the diffractive bifocal lens is equalto the radius of curvature of a monofocal lens having the same power.

[0095] Throughout the example the light distribution between the twofoci was chosen to be 50%:50%, and the target power add for near visionwas +4 D. Other light distributions can be chosen, without changing theprinciples of how the methods work. In practice, light distributionbetween 70%:30% to 30%:70% and near vision add between 3 and 4 dioptershave been on the market. But also outside these ranges the methodsshould be applicable.

[0096] Throughout the example, data from characterization of corneasconducted on a selected population, was used to calculate the resultingcorneal aberrations. The anterior corneal surface shapes of a populationof 71 cataract patients were measured using corneal topography. Thesurface shapes were described using Zernike polynomials. Each surfaceshape was converted into a wavefront aberration. Also the wavefrontaberration was described in Zernike polynomials.

[0097] The method is described in example 4 of the patent application WO01/89424 A1.

[0098] The terms of the Zernike polynomials are expressed in wavelengths(λ), using the reference wavelength of 550 nanometers (λ=550 nm).

[0099] The target in this example is to correct the corneal sphericalaberration by the bifocal IOL. In order to evaluate the designs, atheoretical design cornea was developed, similar to the one described inexample 4 of the patent application WO 01/89424 A1. In the case ofmodelling a monofocal IOL the design cornea can be a 1-surface model,wherein the refractive index of the cornea is the keratometry index of1.3375. For diffractive lenses it is essential to use the real in vivorefractive index surrounding the posterior (diffractive) lens surface.Therefore, a 2-surface model was developed, which has the same on-axisaberrations as the 1-surface model.

[0100] The theoretical performance of the prototype design in terms ofsymmetric Zernike coefficients was evaluated for an IOL having a basepower (far vision) of 20 Diopters. An IOL having this power is close towhat is suitable for most cataract patients. However, the design methodand resulting IOL is similar for other lens powers. Typically, IOLpowers range from 4 to 34 diopters, sometimes extend to −10 to +40diopters and can be occasionally produced even outside these ranges.

Example 1

[0101] In one embodiment, the lens is biconvex, having radii ofcurvature of 12.15 mm on both the anterior and posterior surface and acentral thickness of 1.1 mm. The anterior surface is aspherized. In aniterative process, the aberration of the optical system of design corneaand bifocal IOL are optimised in order to reduce the wavefrontaberration in the far focus position, in this example the Zernike termZ₁₁, representing the spherical aberration. In this process, theasphericity of the anterior lens surface is used as the designparameter. The asphericity of the anterior surface is described by aconic constant. The sag equation of the anterior surface is:${S(r)} = \frac{{cv}*r^{2}}{1 + \sqrt{1 - {{{cv}^{2}\left( {{cc} + 1} \right)}r^{2}}}}$

[0102] wherein cc is the conic constant

[0103] Using commercially available optical design software, thevariable cc can be optimized to minimize the Zernike term Z₁₁ for thefar vision focal point. The variable cc was determined for an aperturesize of 5.1 mm. The anterior surface of this BRAIOL has been modified insuch a way that the spherical aberration of the system (cornea+lens) isnow approximately equal to 0. The resulting value of the conic constantwas −29.32. The Z₁₁ coefficient representing spherical aberration forthe conventional IOL in the eye model is 3.8 λ, while the samecoefficient for the eye model with the designed BRAIOL is 0.01 λ,representing a reduction of the spherical aberration by a factor of 380.The same process as described above for can similarly be performed forany other lens power.

Example 2

[0104] In another embodiment, the lens is biconvex, having radii ofcurvature of 12.15 mm on both the anterior and posterior surface and acentral thickness of 1.1 mm. The diffractive posterior surface isaspherized. In an iterative process, the aberration of the opticalsystem of design cornea and bifocal IOL are optimised in order to reducethe wavefront aberration, in this example the Zernike term Z₁₁,representing the spherical aberration, as well as the symmetrical higherorder terms Z₂₂ and Z₃₇. In this process, the asphericity of theposterior lens surface is used as the design parameter. The asphericityof the posterior surface is described by a conic constant and 2 higherorder terms. The total sag equation is:${S(r)} = {\frac{{cv}*r^{2}}{1 + \sqrt{1 - {{{cv}^{2}\left( {{cc} + 1} \right)}r^{2}}}} + {{ad}*r^{4}} + {{ae}*r^{6}} + {S_{d}(r)}}$

[0105] wherein:

[0106] cc is the conic constant

[0107] ad is the 4^(th) order aspheric coefficient

[0108] ae is the 6^(th) order aspheric coefficient

[0109] Using commercially available optical design software, thevariables cc, ad and ae can be optimized to minimize the Zernike termsZ₁₁, Z₂₂ and Z₃₇ simultaneously in the far focal point. The variablesare determined for an aperture size of 5.1 mm. The posterior surface ofthis BRAIOL has been modified in such a way that the sphericalaberration and the 2 higher order terms of the system (cornea+lens) isnow approximately equal to 0. The optimisation resulted in the posteriorsurface aspheric coefficients presented in table 2: TABLE 2 Asphericcoefficient Value Cc −2.53 Ad   9.4e−4 Ae −5.1e−6

[0110] The optical results can be expressed as a reduction in theZernike coefficients between the conventional BIOL (using cc=ad=ae=0)and the newly designed BRAIOL, and are presented in table 3: TABLE 3Zernike Conventional coefficient BIOL BRAIOL Z₁₁ 3.8 λ 0.01 λ Z₂₂ 0.11 λ−0.003 λ Z₃₇ −0.07 λ −0.07 λ

[0111] Table 3 shows a large reduction of aberration represented by thecoefficients Z₁₁ and Z₂₂ and no significant reduction of coefficientZ₃₇. The same process as described above for can similarly be performedfor any other lens power.

Example 3 Both

[0112] In another embodiment, the lens is biconvex, having an anteriorradius of curvature of 12.15 mm, a posterior radius of curvature of12.59 and a central thickness of 1.1 mm. The diffractive profile islocated on the posterior surface and the anterior surface is aspherized.In an iterative process, the aberration of the optical system of designcornea and bifocal IOL are optimised in order to reduce the wavefrontaberration, in this example the Zernike term Z₁₁, representing thespherical aberration, as well as the symmetrical higher order terms Z₂₂and Z₃₇. In this process, the asphericity of the anterior lens surfaceis used as the design parameter. The asphericity of the anterior surfaceis described by a conic constant and 2 higher order terms. The sagequation of the anterior surface is:${S(r)} = {\frac{{cv}*r^{2}}{1 + \sqrt{1 - {{{cv}^{2}\left( {{cc} + 1} \right)}r^{2}}}} + {{ad}*r^{4}} + {{ae}*r^{6}}}$

[0113] wherein:

[0114] cc is the conic constant

[0115] ad is the 4^(th) order aspheric coefficient

[0116] ae is the 6^(th) order aspheric coefficient

[0117] Using commercially available optical design software, thevariables cc, ad and ae can be optimized to minimize the Zernike termZ₁₁, Z₂₂ and Z₃₇ simultaneously. Furthermore, in this embodiment theZernike terms for both far and near focal points were taken into accountin the optimisation. In this way both far and near focal point wereoptimised simultaneously. As an extra criterion, weight factors wereadded, to secure that the lowest order terms were reduced mostdrastically. The weight factors were 1, 0.1 and 0.01 for Z₁₁, Z₂₄ andZ₃₇ respectively. The variables are determined for an aperture size of5.1 mm. The posterior surface of this BRAIOL has been modified in such away that the spherical aberration and the 2 higher order terms of thesystem (cornea+lens) is now approximately equal to 0. The optimisationresulted in the posterior surface aspheric coefficients, presented intable 4: TABLE 4 Aspheric coefficient Value cc −1.02 ad −4.9e−4 ae−4.9e−5

[0118] The optical results can be expressed as a reduction in theZernike coefficients between the conventional BIOL (using cc=ad=ae=0)and the newly designed BRAIOL. Since both far and near are taken intoaccount, the vector sum of the far and near Zernike coefficients aredisplayed in table 5: TABLE 5 Zernike Conventional coefficient BIOLBRAIOL Z₁₁ 5.3 λ 0.08 λ Z₂₂ 0.15 λ 0.43 λ Z₃₇ 0.08 λ 0.08 λ

[0119] Table 5 shows a large reduction of aberration represented by thecoefficients Z₁₁ and no significant reduction of coefficient Z₂₂ andZ₃₇, indicating that Zernike term Z₁₁ was minimized on the cost of termZ₂₂, while Z₃₇ was as low as reasonably possible already.

[0120] The optical quality was further characterized by calculating themodulation transfer function in the eye model, using an aperture of 5 mm(FIG. 1)

[0121] These calculation results show that, when compared with aconventional BIOL, the modulation transfer function of the BRAIOL isincreased with at least by a factor 2. Prototype lenses of this designwere made and the modulation transfer function was also measured in aneye model. The physical eye model was constructed to have the samewavefront aberrations as the design model based on the population of 71cataract patients. The focal points were determined by focussing at aspatial frequency of 25, 50, 100 cycles per millimetre. FIG. 2 shows theresults. The results are the averages of 8 BRIOL lenses and 10conventional BIOL lenses, with 3 measurements per lens. The FIG. 2confirms the gain in optical quality that can be achieved with theBRAIOL.

[0122] This example clearly shows that the RAIOL design principles canbe successfully applied on bifocal (or multifocal) lenses. Threeapproaches were used: one design with the anterior lens shape optimizedfor Zernike coefficient Z₁₁ for far focus combined with a diffractiveposterior surface. Alternatively a new posterior lens shape wasgenerated by optimizing the wavefront aberrations of Zernikecoefficients Z₁₁, Z₂₂ and Z₃₇. Finally, a new anterior lens shape wasgenerated by optimizing for the Zernike coefficients Z₁₁, Z₂₂ and Z₃₇and for the far as well as the near focus. The performance of these 3types of lenses, in terms of MTF, showed to be essentially comparable.It was also demonstrated that the improvement optical performance ascalculated in theory can be confirmed by measurement of prototypelenses.

[0123] The improvement of the BRAIOL, compared to BIOL (model 811E), issignificant. However the improvement is greater for the larger pupils(larger than 3 mm).

[0124] The optical form chosen for the new BRAIOL design is anequiconvex lens made from a silicone with refractive index of 1.458. Thespherical aberration of an average cornea is balanced by the BRAIOL lensyielding a system without spherical aberration. The front surface of thelens is modified such that the optical path lengths of all on-axis rayswithin the design aperture are the same producing a point focus. Thisfeature can be achieved with many lens forms. The BRAIOL lens couldtherefore be designed on a convex-plano, plano-convex, non-equiconvexlens or any other design yielding a positive lens. The BRAIOL conceptcould also be extended in order to encompass a negative lens used tocorrect the refractive errors of the eye. The front surface or backsurface could also be modified to produce the needed change in opticalpath difference that neutralizes the spherical aberration. There aretherefore many possible designs that would achieve the goals of theBRAIOL lens design.

Example 4 Chromatic Correction of Multifocal Aspheric Intraocular Lenses

[0125] The correction of chromatic aberration is performed by adiffractive lens. A diffractive multifocal lens already has adiffractive profile in its surface. For a bifocal diffractive lens, thisdiffractive profile only has an effect on one of the focal points,usually the near focus. This means that for the near focus, thechromatic aberration is already reduced in some degree, although thiswas not originally intended.

[0126] The chromatic correction by a diffractive lens influences bothfocal points to an (almost) equal amount. Since for bifocal diffractivelenses, the amount of chromatic aberration is not the same in both focalpoints, the amount of chromatic aberration have to be balanced betweenthe two focal points.

[0127] Description of the Lens:

[0128] The example lens is made of silicone material. Its shape isequi-biconvex. The anterior surface of the lens comprises an asphericrefractive lens, on which a diffractive profile is superimposed. Thediffractive profile has a lens power of 2.0 diopters, while the asphericrefractive lens has a lens power of 18.0 D. The total resulting lenspower is 20 diopters. The width (diameter) of the first zone of thediffractive profile is 1.5 mm, and there are 16 rings needed to fill afull 6.0 mm IOL optic. In the periphery of the lens, the diffractiverings are 94 microns apart from each other.

[0129] The posterior surface includes the normal diffractive profilewhich generates a 4 diopter power add in the near focus.

[0130] Eye dimensions, refractive indices and dispersion of the ocularmedia are used as described by Navarro (1985). This eyemodel includes anaspheric cornea. The surface information for the eye model and the lensis given in Table 6. The lens designed is dependent on the eye modelchosen. It must be noted that it is possible to design lenses usingother eye models of actual physiological data from patients. APERTURESRF RADIUS THICKNESS RADIUS MEDIUM NOTE OBJ — 1.00E+20 1.00E+14 AIR 17.72 0.55 2.55 CORNEA ASPHERE 2 6.5 3.05 2.50 AQUEOUS AST — — 2.25AQUEOUS 4 — 0.9 2.25 AQUEOUS 5 13.511 1 2.18 SILICONE ASPHERE,DIFFRACTIVE 6 −13.511 18.30 2.08 VITREOUS DIFFRACTIVE IMS −12 0 1 —RETINA

[0131] Conic and Polynomial Aspheric Data conic Surface constant AD AE 1−0.260000 — — 5 −1.018066 −0.000509 −4.0423e−06

[0132] *Diffractive Surface Data (Symmetric Diffractive Surface) TABLE 6Diffrac- Kinoform Sur- tion construction Kinoform face order Design λorder zone depth DFO DF1 5 1 0.550 μm 1 0.004561 — −0.001

[0133] Behavior of the Lens:

[0134] 38 discrete wavelengths over the visible spectrum of 390 to 760nm (10 nm steps) were used to evaluate the eyemodel including therefractive/diffractive IOL.

[0135] The focus point is here defined as the point where thepolychromatic MTF (Modulation Transfer Function) has its maximum at 50cycles/mm. The polychromatic MTF is determined by the weighed average ofthe MTF results at all wavelengths used. The weighting of thewavelengths was determined by the standard luminance of the eye underphotopic light conditions, which represents the relative sensitivity ofthe retina for different wavelengths. The actual back focal length(ABFL) values for the different wavelengths indicate the presence of achromatic difference in focus and by definition the amount oflongitudinal chromatic aberration. The calculations are performed at a3.0 mm aperture (pupil). FIG. 3 shows the change in focal point versusthe wavelength. The 2 graphs, for far and near vision, are coupled bythe 4 diopter diffractive power add. Especially for wavelengths higherthan 550 nm, this example design shows a good balance between thechromatic aberration of the far and the near focal point.

[0136] Table 7 and FIGS. 4A and 4B show the modulations at 50 cycles permillimeters for a spherical lens diffractive bifocal lens, a diffractivebifocal lens with an aspherical anterior surface and a diffractivebifocal lens with an aspherical anterior surface with also the chromaticaberration corrected by a 2.0 D monofocal diffractive pattern on theanterior surface. The chromatic correction mainly influences the FARfocal point, since the NEAR focal point is already (in part) correctedby the diffractive bifocal surface. TABLE 7 monochromatic polychromaticMTF at 50 c/mm MTF at 50 c/mm FAR NEAR Limit FAR NEAR Limit Spherical0.33 0.30 0.83 0.23 0.28 0.83 Aspherical 0.34 0.34 0.83 0.23 0.31 0.83Aspherical, chromatic 0.33 0.34 0.83 0.29 0.31 0.83 corrected

[0137] A number of embodiments have been described above. However, it isobvious that the design could be varied without deviating from theinventive idea of providing a multifocal ophthalmic lens correctingaberration in the eye system.

[0138] Therefore the present invention should not be regarded asrestricted to the above disclosed embodiments, but can be varied withinthe scope of the appended claims. For example, the BIOL can be designedto compensate for non-symmetrical Zernike terms. This would requiremaking surfaces being rotationally non-symmetric, which is within thestate of the art production techniques, demonstrated by cylindricallenses being currently on the market.

1. A method of designing a multifocal ophthalmic lens with one basefocus and at least one additional focus, capable of reducing aberrationsof the eye for at least one of the foci after its implantation,comprising the steps of: (i) characterizing at least one corneal surfaceas a mathematical model; (ii) calculating the resulting aberrations ofsaid corneal surface(s) by employing said mathematical model; (iii)modelling the multifocal ophthalmic lens such that a wavefront arrivingfrom an optical system comprising said lens and said at least onecorneal surface obtains reduced aberrations for at least one of thefoci.
 2. A method according to claim 1, wherein the ophthalmic lens is amultifocal intraocular lens.
 3. A method according to claim 1 or 2,comprising determining the resulting aberrations of said cornealsurface(s) in terms of a wavefront having passed said cornea.
 4. Amethod according to any of the claims 1 to 3, wherein said cornealsurface(s) is(are) characterized in terms of a conoid of rotation.
 5. Amethod according to any of the claims 1 to 3 wherein said cornealsurface(s) is(are) characterized in terms of polynomials.
 6. A methodaccording to claim 5, wherein said corneal surface(s) is(are)characterized in terms of a linear combination of polynomials.
 7. Amethod according to any of the preceding claims, wherein said opticalsystem. further comprises complementary means for optical correction,such as spectacles or an ophthalmic correction lens.
 8. A methodaccording to any of the preceding claims, wherein estimations of cornealrefractive power and axial eye length designate the selection of theoptical powers for the multifocal intraocular lens.
 9. A methodaccording to any of the preceding claims, wherein the multifocalintraocular lens is modelled by selecting a suitable aspheric componentfor the anterior surface.
 10. A method according to any of the precedingclaims, including characterizing the front corneal surface of anindividual by means of topographical measurements and expressing thecorneal aberrations as a combination of polynomials.
 11. A methodaccording to any of the preceding claims, including characterizing frontand rear corneal surfaces of an individual by means of topographicalmeasurements and expressing the total corneal aberrations as acombination of polynomials.
 12. A method according to any of thepreceding claims, including characterizing corneal surfaces of aselected population and expressing average corneal aberrations of saidpopulation as a combination of polynomials.
 13. A method according toany of the preceding claims, comprising the further steps of: (vii)calculating the aberrations resulting from an optical system comprisingsaid modelled intraocular lens and cornea; (iix) determining if themodelled intraocular lens has provided sufficient reduction inaberrations; and optionally re-modelling the intraocular lens until asufficient reduction is obtained.
 14. A method according to claim 13,wherein said aberrations are expressed as a linear combination ofpolynomials.
 15. A method according to claim 13 or 14, wherein there-modelling includes modifying one or several of the anterior surfaceshape and central radius, the posterior surface shape and centralradius, lens thickness and refractive index of the lens.
 16. A methodaccording to any of the claims 14 to 15, wherein the re-modellingincludes modifying the anterior surface of the lens.
 17. A methodaccording to any of the claims 14 to 16, wherein said polynomials areSeidel or Zernike polynomials.
 18. A method according to claim 17,comprising modelling a lens such that an optical system comprising saidmodel of intraocular lens and cornea provides reduction of sphericalterms as expressed in Seidel or Zernike polynomials in a wave fronthaving passed through the system.
 19. A method according to claim 17 or18, comprising the steps of: expressing the corneal aberrations as alinear combination of Zernike polynomials; determining the cornealwavefront Zernike coefficients; modelling the multifocal intraocularlens such that an optical system comprising said model lens and corneaprovides a wavefront having a sufficient reduction of Zernikecoefficients in at least 1 of the foci.
 20. A method according to claim19, further comprising the steps of: calculating the Zernikecoefficients of a wavefront resulting from an optical system comprisingthe modelled multifocal intraocular lens and cornea; determining if saidintraocular lens has provided a sufficient reduction of Zernikecoefficients; and optionally re-modelling said lens until a sufficientreduction is said coefficients are obtained.
 21. A method according toclaim 20, comprising sufficiently reducing Zernike coefficientsreferring to spherical aberration.
 22. A method according to any of theclaims 19 to 21 comprising sufficiently reducing Zernike coefficientsreferring to aberrations above the fourth order.
 23. A method accordingto any of the claims 19 to 22 comprising sufficiently reducing the 11thZernike coefficient of a wavefront front from an optical systemcomprising cornea and said modelled intraocular lens, so as to obtain aneye sufficiently free from spherical aberration.
 24. A method accordingto any of the preceding claims, wherein the reduction of aberrations isoptimized for one of the foci.
 25. A method according to claim 24,wherein the reduction of aberrations is optimized for the base focus.26. A method according to claim 24, wherein the reduction of aberrationsis optimized for one of the at least one additional focus.
 27. A methodaccording to any of the claims 1 to 23, wherein the reduction ofaberrations is optimized for the base focus and the at least oneadditional focus, simultaneously.
 28. A method according to any of thepreceding claims, wherein the modelling of the multifocal intraocularlens comprises modelling the lens as a multifocal lens of diffractivetype.
 29. A method according to claim 28, wherein the diffractivepattern is formed on the anterior and/or posterior surface of the lens.30. A method according to claim 29, wherein the diffractive pattern isformed on the lens surface that is modelled to reduce aberrations of theoptical system.
 31. A method according to claim 29, wherein thediffractive pattern is formed on one surface of the lens and the othersurface of the lens is modelled to reduce aberrations of the opticalsystem.
 32. A method according to any of the claims 1 to 28, wherein themodelling of the multifocal intraocular lens comprises modelling thelens as a multifocal lens of refractive type with annular rings withdifferent radii of curvatures.
 33. A method according to claim 32wherein the annular rings are formed on the lens surface that ismodelled to reduce aberrations of the optical system.
 34. A methodaccording to claim 32 wherein the annular rings are formed on onesurface of the lens and the other surface is modelled to reduceaberrations of the optical system.
 35. A method according to any of theclaims 1 to 34, wherein the modelling of the multifocal intraocular lenscomprises modelling a bifocal lens.
 36. A method according to any of theclaims 1 to 35, wherein the modeling of the multifocal intraocular lensprovides a lens with substantially the same reduced aberrations for allfoci.
 37. A method according to any of the claims 1 to 36, wherein thesum of the modulation for the two or more foci is more than 0.40, at aspatial frequency of 50 cycles per millimetre, when the measurements areperformed in an average/individual eye model using a 5 mm aperture. 38.A method according to claim 37, wherein the sum of the modulation forthe two or more foci is more than 0.50.
 39. A method according to claim37 or 38, wherein the modelling of the multifocal intraocular lenscomprises modelling a bifocal lens with a light distribution of 50-50%between the two foci, and the modulation is at least 0.2 for each focus.40. A method of selecting a multifocal intraocular lens that is capableof reducing aberrations of the eye for at least one of the foci afterits implantation comprising the steps of: (i) characterizing at leastone corneal surface as a mathematical model; (ii) calculating theresulting aberrations of said corneal surfaces(s) by employing saidmathematical model; (iii) selecting an intraocular lens having asuitable configuration of optical powers from a plurality of lenseshaving the same power configurations, but different aberrations; (iv)determining if an optical system comprising said selected lens andcorneal model sufficiently reduces the aberrations.
 41. A methodaccording to claim 40, comprising determining the resulting aberrationsof said corneal surface(s) in a wavefront having passed said cornea. 42.A method according to claim 40 or 41 further comprising the steps of:(v) calculating the aberrations of a wave front arriving from an opticalsystem of said selected lens and corneal model; (vi) determining if saidselected multifocal intraocular lens has provided a sufficient reductionin aberrations in a wavefront arriving from said optical system for atleast one of the foci; and optionally repeating steps (iii) and (iv) byselecting at least one new lens having the same optical power untilfinding a lens capable of sufficiently reducing the aberrations.
 43. Amethod according to any of the claims 40 to 42, wherein said cornealsurface(s) is(are) characterized in terms of a conoid of rotation.
 44. Amethod according to any of the claims 40 to 42 wherein said cornealsurface(s) is(are) characterized in terms of polynomials.
 45. A methodaccording to any of the claims 40 to 42, wherein said corneal surface(s)is(are) characterized in terms of a linear combination of polynomials.46. A method according to any of the claims 40 to 45, wherein saidoptical system further comprises complementary means for opticalcorrection, such as spectacles or an ophthalmic correction lens.
 47. Amethod according to any of the claims 40 to 46, wherein cornealrefractive power and axial eye length estimations designate theselection of lens optical powers for the multifocal intraocular lens.48. A method according to claim 39 or 45, wherein an optical systemcomprising said corneal model and selected multifocal intraocular lensprovides for a wavefront substantially reduced from aberrations for atleast one of the foci, as expressed by at least one of said polynomials.49. A method according to any of the claims 40 to 48 includingcharacterizing the front corneal surface of an individual by means oftopographical measurements and expressing the corneal aberrations as acombination of polynomials.
 50. A method according to any of the claims40 to 49 including characterizing front and rear corneal surfaces of anindividual by means of topographical measurements and expressing thetotal corneal aberrations as a combination of polynomials.
 51. A methodaccording to any of the claims 40 to 46, including characterizingcorneal surfaces of a selected population and expressing average cornealaberrations of said population as a combination of polynomials.
 52. Amethod according to claim 45 or 51, wherein said polynomials are Seidelor Zernike polynomials.
 53. A method according to claim 52, comprisingthe steps of: (i) expressing the corneal aberrations as a linearcombination of Zernike polynomials; (ii) determining the corneal Zernikecoefficients; (iii) selecting the multifocal intraocular lens such thatan optical system comprising said lens and cornea provides a wavefronthaving a sufficient reduction in Zernike coefficients for at least oneof the foci.
 54. A method according to claim 53, further comprising thesteps of: (iv) calculating the Zernike coefficients resulting from anoptical system comprising the modelled multifocal intraocular lens andcornea; (v) determining if said intraocular lens has provided areduction of Zernike coefficients; and optionally selecting a new lensuntil a sufficient reduction is said coefficients is obtained.
 55. Amethod according to claim 53 or 54, comprising determining Zernikepolynomials up to the 4^(th) order.
 56. A method according to any of theclaims 53 to 55 comprising sufficiently reducing Zernike coefficientsreferring to spherical aberration.
 57. A method according to any of theclaims 53 to 56 comprising sufficiently reducing Zernike coefficientsabove the fourth order.
 58. A method according to any of the claims 53to 57 comprising sufficiently reducing the 11th Zernike coefficient of awavefront front from an optical system comprising model cornea and saidselected intraocular lens, so as to obtain an eye sufficiently free fromspherical aberration for at least one of the foci.
 59. A methodaccording to any of the claims 53 to 58 comprising selecting aintraocular lens such that an optical system comprising said intraocularlens and cornea provides reduction of spherical aberration terms asexpressed in Seidel or Zernike polynomials in a wave front having passedthrough the system.
 60. A method according to any of the claims 53 to59, wherein reduction in higher aberration terms is accomplished.
 61. Amethod according to any of the claims 40 to 60 characterized byselecting a multifocal intraocular lens from a kit comprising lenseswith a suitable range of power configurations and within each range ofpower configurations a plurality of lenses having different aberrations.62. A method according to claim 61, wherein said aberrations arespherical aberrations.
 63. A method according to claim 62, wherein saidlenses within each range of power configurations have surfaces withdifferent aspheric components.
 64. A method according to claim 63,wherein said surfaces are the anterior surfaces.
 65. A method accordingto any of the claims 40 to 64, wherein the reduction of aberrations isoptimized for one of the foci.
 66. A method according to claim 65,wherein the reduction of aberrations is optimized for the base focus.67. A method according to claim 65, wherein the reduction of aberrationsis optimized for one of the at least one additional focus.
 68. A methodaccording to any of the claims 40 to 64, wherein the reduction ofaberrations is optimized for the base focus and the at least oneadditional focus, simultaneously.
 69. A method according to any of theclaims 40 to 68, wherein the multifocal intraocular lens is a multifocallens of diffractive type.
 70. A method according to claim 69, whereinthe diffractive pattern is formed on the anterior and/or posteriorsurface of the lens.
 71. A method according to claim 70, wherein thediffractive pattern is formed on the lens surface that is modelled toreduce aberrations of the optical system.
 72. A method according toclaim 70, wherein the diffractive pattern is formed on one surface ofthe lens and the other surface of the lens is modelled to reduceaberrations of the optical system.
 73. A method according to any of theclaims 40 to 68, wherein the multifocal intraocular lens is a multifocallens of refractive type with annular rings with different radii ofcurvatures.
 74. A method according to claim 73 wherein the annular ringsare formed on the lens surface that is modelled to reduce aberrations ofthe optical system.
 75. A method according to claim 73 wherein theannular rings are formed on one surface of the lens and the othersurface is modelled to reduce aberrations of the optical system.
 76. Amethod according to any of the claims 40 to 75, wherein the multifocalintraocular lens is a bifocal lens.
 77. A method according to any of theclaims 40 to 35, wherein the multifocal intraocular lens hassubstantially the same reduced aberrations for all foci.
 78. A methodaccording to any of the claims 40 to 77, wherein the sum of themodulation for the two or more foci is more than 0.40, at a spatialfrequency of 50 cycles per millimetre, when the measurements areperformed in an average/individual eye model using a 5 mm aperture. 79.A method according to claim 78, wherein the sum of the modulation forthe two or more foci is more than 0.50.
 80. A method according to claim78 or 79, wherein the lens is bifocal with a light distribution of50-50% between the two foci and the modulation is at least 0.2 for eachfocus.
 81. A method of designing a multifocal ophthalmic lens suitablefor implantation into the eye, characterized by the steps of: selectinga representative group of patients; collecting corneal topographic datafor each subject in the group; transferring said data to termsrepresenting the corneal surface shape of each subject for a presetaperture size; calculating a mean value of at least one corneal surfaceshape term of said group, so as to obtain at least one mean cornealsurface shape term and/or calculating a mean value of at least one tothe cornea corresponding corneal wavefront aberration term, each cornealwavefront aberration term being obtained by transforming correspondingthrough corneal surface shape terms; from said at least one mean cornealsurface shape term or from said at least one mean corneal wavefrontaberration term designing a multifocal ophthalmic lens capable ofreducing said at least one mean wavefront aberration term of the opticalsystem comprising cornea and lens for at least one of the foci. 82.Method according to claim 81, characterized in that it further comprisesthe steps of: designing an average corneal model for the group of peoplefrom the calculated at least one mean corneal surface shape term or fromthe at least one mean corneal wavefront aberration term; checking thatthe designed multifocal ophthalmic lens compensates correctly for the atleast one mean aberration term for at least one of the foci by measuringthese specific aberration terms of a wavefront having travelled throughthe model average cornea and the lens and redesigning the multifocallens if said at least one aberration term not has been sufficientlyreduced in the measured wavefront.
 83. Method according to claim 81 or82, characterized by calculating an aspheric surface descriptiveconstant for the lens to be designed from the mean corneal surface shapeterms or from the mean corneal wavefront aberration terms for apredetermined radius.
 84. Method according to any one of the claims81-83, characterized by selecting people in a specific age interval toconstitute the group of people.
 85. Method according to any one of theclaims 81-84, characterized by selecting people who will undergo acataract surgery to constitute the group of people.
 86. Method accordingto any one of the claims 81-85, characterized by designing the lensspecifically for a patient that has undergone corneal surgery andtherefore selecting people who have undergone corneal surgery toconstitute the group of people.
 87. Method according to any one of theclaims 81-86, characterized by selecting people who have a specificocular disease to constitute the group of people.
 88. Method accordingto any one of the claims 81-87, characterized by selecting people whohave a specific ocular optical defect to constitute the group of people.89. Method according to any one of the claims 81-88, characterized inthat it further comprises the steps of: measuring the at least onewavefront aberration term of one specific patient's cornea; determiningif the selected group corresponding to this patient is representativefor this specific patient and if this is the case implant the multifocallens designed from these average values and if this not is the caseimplant a multifocal lens designed from average values from anothergroup or design an individual lens for this patient.
 90. Methodaccording to any one of the claims 81-89, characterized by providing themultifocal lens with at least one nonspherical surface that reduces atleast one positive aberration term of an incoming nonspherical wavefrontfor at least one of the foci.
 91. Method according to claim 90,characterized in that said positive aberration term is a positivespherical aberration term.
 92. Method according to any one of the claims81-91, characterized by providing the multifocal lens with at least onenonspherical surface that reduces at least one term of a Zernikepolynomial representing the aberration of an incoming nonsphericalwavefront for at least one of the foci.
 93. Method according to claim92, characterized by providing the lens with at least one nonsphericalsurface that reduces the 11th normalized Zernike term representing thespherical aberration of an incoming nonspherical wavefront.
 94. A methodaccording to any of claims 81-93 characterized by designing a multifocallens to reduce, for at least one of the foci, spherical aberration in awavefront arriving from an average corneal surface having the formula:$z = {\frac{\left( \frac{1}{R} \right)r^{2}}{1 + \sqrt{1 - {\left( \frac{1}{R} \right)^{2}\left( {{cc} + 1} \right)r^{2}}}} + {{ad}\quad r^{4}} + {{ae}\quad r^{6}}}$

wherein the conical constant cc has a value ranging between −1 and 0, Ris the central corneal radius and ad and ae are aspheric constants. 95.A method according to claim 94, wherein the conical constant (cc) rangesfrom about −0.05 for an aperture size (pupillary diameter) of 4 mm toabout −0.18 for an aperture size of 7 mm.
 96. Method according to claim81-95, characterized by providing the multifocal lens with a surfacedescribed by a conoid of rotation modified conoid having a conicalconstant (cc) less than
 0. 97. Method according to any one of the claims81-96, characterized by providing the multifocal lens with a, for thepatient, suitable power configuration,.
 98. Method according to any oneof the claims 81-97, characterized by designing the multifocal lens tobalance, for at least one of the foci, the spherical aberration of acornea that has a Zernike polynomial coefficient representing sphericalaberration of the wavefront aberration with a value in the interval from0.0000698 mm to 0.000871 mm for a 3 mm aperture radius.
 99. Methodaccording to any one of the claims 81-97, characterized by designing themultifocal lens to balance, for at least one of the foci, the sphericalaberration of a cornea that has a Zernike polynomial coefficientrepresenting spherical aberration of the wavefront aberration with avalue in the interval from 0.0000161 mm to 0.000200 mm for a 2 mmaperture radius.
 100. Method according to any one of the claims 81-97,characterized by designing the multifocal lens to balance, for at leastone of the foci, the spherical aberration of a cornea that has a Zernikepolynomial coefficient representing spherical aberration of thewavefront aberration with a value in the interval from 0.0000465 mm to0.000419 mm for a 2.5 mm aperture radius.
 101. Method according to anyone of the claims 81-97, characterized by designing the multifocal lensto balance, for at least one of the foci, the spherical aberration of acornea that has a Zernike polynomial coefficient representing sphericalaberration of the wavefront aberration with a value in the interval from0.0000868 mm to 0.00163 mm for a 3.5 mm aperture radius.
 102. Amultifocal ophthalmic lens obtained in accordance with any of thepreceding claims, capable of, for at least one of its foci, transferringa wavefront having passed through the cornea of the eye into asubstantially spherical wavefront having its centre in the retina of theeye.
 103. A multifocal ophthalmic lens with one base focus and at leastone additional focus, characterized in that the shape of the lens ismodelled such that the resulting aberrations are reduced for at leastone of the foci in an optical system comprising said multifocal lens anda model cornea having aberration terms, or being without aberrationterms.
 104. A multifocal intraocular lens according to claim
 103. 105. Amultifocal intraocular lens according to claim 104 wherein said cornealmodel includes average aberration terms calculated from characterizingindividual corneas for a suitable population, and expressing them inmathematical terms so as to obtain individual aberration terms.
 106. Amultifocal intraocular lens according to claim 105, wherein saidaberration terms is a linear combination of Zernike polynomials.
 107. Amultifocal intraocular lens according to claim 106 capable of reducingaberration terms expressed in Zernike polynomials of said corneal model,such that a wavefront arriving from an optical system comprising saidmodel cornea and said lens obtains substantially reduced sphericalaberration.
 108. A multifocal intraocular lens according to claim 107capable of reducing the 11th Zernike term of the 4th order.
 109. Amultifocal intraocular lens according to any of the claims 103 to 108,adapted to replace the natural lens in a patient's eye, said multifocalintraocular lens having at least one nonspherical surface, this at leastone nonspherical surface being designed such that the lens for at leastone of the foci, in the context of the eye, provides to a passingwavefront at least one wavefront aberration term having substantiallythe same value but with opposite sign to a mean value of the sameaberration term obtained from corneal measurements of a selected groupof people, to which said patient is categorized, such that a wavefrontarriving from the cornea of the patient's eye obtains a reduction insaid at least one aberration term provided by the cornea after passingsaid lens.
 110. A multifocal intraocular lens according to claim 109,characterized in that the nonspherical surface of the lens is designedto reduce at least one positive aberration term of a passing wavefront.111. A multifocal intraocular lens according to claim 109 or 110,characterized in that the at least one wavefront aberration termprovided to the passing wavefront by the lens is a spherical aberrationterm, such that a wavefront arriving from the cornea of the patient'seye obtains a reduction in said spherical aberration term provided bythe cornea after passing said lens.
 112. A multifocal intraocular lensaccording to any one of the claims 109 to 111, characterized in that theat least one wavefront aberration term provided to the passing wavefrontby the lens is at least one term of a Zernike polynomial representingthe wavefront aberration of the cornea.
 113. A multifocal intraocularlens according to claim 112, characterized in that the at least onewavefront aberration term provided to the passing wavefront by the lensis the 11th normalized Zernike term of a wavefront aberration of thecornea.
 114. A multifocal intraocular lens according to any one of theclaims 105-113, characterized in that said selected group of people is agroup of people belonging to a specific age interval.
 115. A multifocalintraocular lens according to any one of the claims 105-114,characterized in that the lens is adapted to be used by a patient thathas undergone corneal surgery and in that said selected group of peopleis a group of people who have undergone corneal surgery.
 116. Amultifocal intraocular lens according to any one of the claims 105-115,characterized in that said selected group of people is a group of peoplewho will undergo a cataract surgical operation.
 117. A multifocalintraocular lens according to claim 109 or 110 characterized in that thenonspherical surface is a modified conoid surface having a conicalconstant (cc) less than zero.
 118. An multifocal intraocular accordingto claim 117 characterized in that it, for at least one of the foci, iscapable of eliminating or substantially reducing spherical aberration ofa wavefront in the eye or in an eye model arriving from a prolatesurface having the formula:$z = {\frac{\left( \frac{1}{R} \right)r^{2}}{1 + \sqrt{1 - {\left( \frac{1}{R} \right)^{2}\left( {{cc} + 1} \right)r^{2}}}} + {{ad}\quad r^{4}} + {{ae}\quad r^{6}}}$

the conical constant cc has a value ranging between −1 and 0, R is thecentral corneal radius and ad and ae are aspheric constants.
 119. Amultifocal intraocular lens according to any one of the claims 109-118,characterized in that one of the at least one nonspherical surface ofthe lens is the anterior surface.
 120. A multifocal intraocular lensaccording to any one of the claims 109-118, characterized in that one ofthe at least one nonspherical surface of the lens is the posteriorsurface.
 121. A multifocal intraocular lens according to any of theclaims 104-120, characterized in that the reduction of aberrations isoptimized for one of the foci.
 122. A multifocal intraocular lensaccording to claim 121, characterized in that the reduction ofaberrations is optimized for the base focus.
 123. A multifocalintraocular lens according to claim 121, characterized in that thereduction of aberrations is optimized for one of the at least oneadditional focus.
 124. A multifocal intraocular lens according to any ofthe claims 104 to 120, characterized in that the reduction ofaberrations is optimized for the base focus and the at least oneadditional focus, simultaneously.
 125. A multifocal intraocular lensaccording to any of the claims 104 to 124, characterized in that it isof diffractive type.
 126. A multifocal intraocular lens according toclaim 125, characterized in that the diffractive pattern is formed onthe anterior and/or posterior surface of the lens.
 127. A multifocalintraocular lens according to claim 125, characterized in that thediffractive pattern is formed on the lens surface that is modelled toreduce aberrations of the optical system.
 128. A multifocal intraocularlens according to claim 125, characterized in that the diffractivepattern is formed on one surface of the lens and the other surface ofthe lens is modelled to reduce aberrations of the optical system.
 129. Amultifocal intraocular lens according to any of the claims 104 to 124,characterized in that it is of refractive type with annular rings withdifferent radii of curvatures.
 130. A multifocal intraocular lensaccording to claim 129 characterized in that the annular rings areformed on the lens surface that is modelled to reduce aberrations of theoptical system.
 131. A multifocal intraocular lens according to claim129 characterized in that the annular rings are formed on one surface ofthe lens and the other surface is modelled to reduce aberrations of theoptical system.
 132. A multifocal intraocular lens according to any ofthe claims 104 to 131, characterized in that it is bifocal.
 133. Amultifocal intraocular lens according to any one of the claims 104 to132, characterized in that the lens is made from a soft biocompatiblematerial.
 134. A multifocal intraocular lens according to any one of theclaims 104 to 133, characterized in that the lens is made of a siliconematerial.
 135. A multifocal intraocular lens according to claim 134,characterized in that the silicone material is characterized by arefractive index larger than or equal to 1.43 at a wavelength of 546 nm,an elongation of at least 350%, a tensile strength of at least 300 psiand a shore hardness of about 30 as measured with a Shore Type ADurometer.
 136. A multifocal intraocular lens according to any one ofthe claims 104 to 133, characterized in that the lens is made ofhydrogel.
 137. A multifocal intraocular lens according to any one of theclaims 104 to 132, characterized in that the lens is made of a rigidbiocompatible material.
 138. A multifocal intraocular lens according toany one of the claims 104 to 137, characterized in that it is designedto balance the spherical aberration of a cornea that has a Zernikepolynomial coefficient representing spherical aberration of thewavefront aberration with a value in the interval from 0.0000698 mm to0.000871 mm for a 3 mm aperture radius.
 139. A multifocal intraocularlens according to any one of the claims 104 to 137, characterized inthat it is designed to balance the spherical aberration of a cornea thathas a Zernike polynomial coefficient representing spherical aberrationof the wavefront aberration with a value in the interval from 0.0000161mm to 0.000200 mm for a 2 mm aperture radius.
 140. A multifocalintraocular lens according to any one of the claims 104 to 137,characterized in that it is designed to balance the spherical aberrationof a cornea that has a Zernike polynomial coefficient representingspherical aberration of the wavefront aberration with a value in theinterval from 0.0000465 mm to 0.000419 mm for a 2.5 mm aperture radius.141. A multifocal intraocular lens according to any one of the claims104 to 137, characterized in that it is designed to balance thespherical aberration of a cornea that has a Zernike polynomialcoefficient representing spherical aberration of the wavefrontaberration with a value in the interval from 0.0000868 mm to 0.00163 mmfor a 3.5 mm aperture radius.
 142. A multifocal intraocular lensaccording to any one of the claims 104 to 141, characterized in that itis designed to provide substantially the same reduced aberrations forall foci.
 143. A multifocal intraocular lens according to any one of theclaims 104 to 142 characterized in that the sum of the modulation forthe two or more foci is more than 0.40, at a spatial frequency of 50cycles per millimetre, when measured performed in an average/individualeye model using a 5 mm aperture.
 144. A multifocal intraocular lensaccording to claim 143 characterized in that the sum of the modulationfor the two or more foci is more than 0.50.
 145. A multifocalintraocular lens according to claim 143 or 144, characterized in that itis bifocal with a light distribution of 50-50% between the two focihaving a modulation of at least 0.2 for each focus.
 146. A multifocallens according to any of claims 126 to 145 that is bifocal having alight distribution other than 50-50% obtained from reducing the stepheight of the diffractive pattern in the direction towards the lensperiphery, so more light intensity is shifted to the distant focus thanthe near focus.
 147. A multifocal lens according to claim 146 having agradually reduced step height towards the lens periphery.
 148. Amultifocal lens according to claim 147 having a zone wherein the stepheight gradually reduces towards the lens periphery.
 149. A multifocallens according to claim 148 wherein said zone is located in the lensperiphery.
 150. A multifocal lens according to any of claims 102 or 103to 149 characterized in that it comprises at least one surfaceconfigured to compensate a passing wavefront from chromatic aberrationas introduced by the optical surfaces of the eye and the lens itself, sochromatic aberration is reduced for at least one of the foci comprisingsaid multifocal lens.
 151. A refractive multifocal lens according toclaim 150 characterized in that said at least one surface is configuredas a diffractive part with a diffractive surface pattern and has arefractive power to be added to the total lens power.
 152. A multifocallens according to claim 150 having a first diffractive pattern capableof generating multiple foci, wherein said surface is configured asdiffractive part with a second diffractive surface pattern and has arefractive power to be added to the total lens power.
 153. A multifocallens according claim 152, that is a bifocal lens, wherein the seconddiffractive surface pattern consists of a number rings of which thefirst zone has a radial width of 1.5 mm for 20 D total lens power. 154.A multifocal lens according to claim 152 or 153, wherein the seconddiffractive surface pattern is located on the anterior side of lens.155. A multifocal lens according to claims 150 to 154 that is bifocaland has a correction for chromatic aberration that is balanced betweenthe two foci in a manner that polychromatic modulation transferfunctions at 50 cycles/mm obtained from a set eye model approaches thesame value.
 156. A multifocal lens according to claim 103 characterizedin that it has at least one nonspherical surface construed so it reducessuch aberrations in a wavefront passing said lens that are generatedfrom the lens itself.
 157. A multifocal lens according to claim 156characterized in that it reduces spherical aberrration.
 158. Amultifocal lens according to claim 156 and 157 characterized in that isof the diffractive type having a diffractive pattern on the lens surfacethat is capable of generating multiple foci.
 159. A multifocal lensaccording to claims 158 characterized in that it is a bifocal lens thatdistributes more light to its distant focus than to its near focus. 160.A multifocal ophthalmic lens having at least one nonspherical surfacewhich when expressed as a linear combination of polynomial termsrepresenting its aberrations is capable of reducing similar suchaberration terms obtained in a wavefront having passed the cornea,thereby obtaining an eye sufficiently free from aberrations.
 161. A lensaccording to claim 160, wherein said nonspherical surface is theanterior surface of the lens.
 162. A lens according to claim 161,wherein said nonspherical surface is the posterior surface of the lens.163. A lens according to any one of the claims 160 to 162, being amultifocal intraocular lens.
 164. A lens according to any one of theclaims 160 to 163, wherein said polynomial terms are Zernikepolynomials.
 165. A lens according to claim 164 capable of reducingpolynomial terms representing spherical aberrations and astigmatism.166. A lens according to claim 165, capable of reducing the 11th Zernikepolynomial term of the 4th order.
 167. A lens according to any one ofthe claims 160 to 166 made from a soft biocompatible material.
 168. Alens according to claim 167 made of silicone.
 169. A lens according toclaim 167 made of hydrogel.
 170. A lens according any one of the claims160 to 166 made of a rigid biocompatible material.
 171. Multifocalintraocular lens according to any of the claims 104 to 170,characterized in that it is a bifocal intraocular lens of diffractivetype with a nonspherical anterior surface, and a diffractive patternformed on the posterior surface.
 172. Multifocal intraocular lensaccording to claim 171 characterized in that it has a light distributionof 50-50% between the two foci.
 173. Multifocal intraocular lensaccording to claim 171 characterized in that it has a light distributionof 60-40% between the two foci.
 174. Multifocal intraocular lensaccording to claim 171 characterized in that it has a light distributionof 40-60% between the two foci.